Recent discovery that similar peptides are present in the brain and in nerve fibers and endocrine cells in the gastrointestinal tract has led to numerous hyoptheses regarding the neurocrine, paracrine, and endocrine roles of these peptides in gastrointestinal physiology. Evidence has been obtained that several of these peptides exist in two or more biologically active forms within the same tissue in a single species and that corresponding peptides may differ in structure between mammalian species. The biological significance of structural differences cannot be determined until these peptides have been fully characterized in more than one mammalian species. The object of this proposal is to characterize several neuronal neuropeptides from the dog. Although this species is used extensively in physiological studies, none of the canine neuropeptides have been purified sufficiently to permit structural analysis. In preliminary studies I have determined that the muscle layer of canine small intestine contains two or more molecular forms of peptides that crossreact in radioimmunoassays developed for porcine VIP, somatostatin, CCK8, and amphibian bombesin. These immunoreactive peptides will be purified completely by gel permeation, ion exchange, affinity, and high pressure liquid chromatography. Their amino acid compositions and sequences will be determined. Biological and immunochemical properties of these pure peptides will be compared with properties of natural and synthetic porcine and amphibian peptides. More complete studies of biological and immunological properties will be made possible by synthesis of large amounts of canine neuropeptides based on these structural studies. Improved methodology for purification of these peptides from relatively small amounts of starting material should permit characterization of corresponding human peptides.